1. Field of the Invention
This invention relates to a fixing apparatus used for fixing a toner image transferred onto a sheet of paper provided in an electrophotographic printing machine or the like.
2. Description of the Related Art
Fixing apparatuses of the above identified type normally comprise a fixing roller and a pressurizing roller held in contact with the fixing roller so as to apply pressure to it. The sheet of paper onto which a toner image has been transferred is then fed to the nip section defined between the fixing roller and the pressurizing roller. The toner image on the sheet of paper is fixed to the latter as the sheet passes through the nip section.
The fixing roller is provided in the inside thereof with a heater, which heats the fixing roller from inside. However, such a fixing roller is accompanied by a disadvantage that it takes much time for the inside heater to heat the fixing roller until the temperature of the outer surface of the roller reaches the level necessary for fixation.
Recently, there has been developed a fixing apparatus in which a heating roller is arranged at a position separated from the fixing roller so as to hold a thin heat transfer belt with the fixing roller. With such a fixing apparatus, heat generated by the heating roller is transferred to the outer surface of the fixing roller by way of the thin heat transfer belt so that the temperature of the outer surface of the fixing roller can be raised to the necessary level in a short period of time.
However, in a fixing apparatus comprising such a heat transfer belt, the sheet of paper, onto which a toner image has been transferred, may adhere to the heat transfer belt during the fixing operation. Therefore, such fixing apparatuses are provided with a release member, which releases the sheet of paper from the heat transfer belt.
However, when a high density image is transferred to an area of the sheet of paper located near the front end of the sheet as viewed in the moving direction of the sheet, a release error can easily occur if compared with a sheet of paper where a low density image is transferred to the same area. Then, the sheet of paper adheres to the fixing belt.
When the sheet of paper adheres to the fixing belt, it either completely sticks to the corresponding surface of the fixing belt or comes off by itself from the fixing belt at a location where the fixing belt held by the heating roller turns with a small radius of curvature and becomes retained in a space near the fixing belt.
However, as the sheet of paper is retained in such a space, it may not be found by the user, thus often remains there unnoticed. The sheet of paper that is left in such a space is then exposed to high temperatures for a long period of time, and eventually catches fire, which can in turn damage the fixing belt.